JP2010091895A - Active matrix display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active matrix display device having a driving frequency as low as possible. <P>SOLUTION: The active matrix display device 1 includes: a plurality of pixel arrays 10 and a backlight light source 12 irradiating the plurality of pixels to display an image including a plurality of frames. The display device 1 includes: a plurality of optical shutters provided for each of the plurality of pixels; a shutter control unit 14 for opening and closing the plurality of optical shutters; a light source control unit 16 modulating the intensity of light emitted from the light source 12 into two or more multiple levels; and a synchronization control unit 18 synchronizing the intensity modulation of the light emitted from the light source 12 by the light source control unit 16 with the opening and closing of the plurality of optical shutters by the shutter control unit 14 so as to achieve a predetermined grayscale representation in one predetermined frame. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an active matrix display device that includes an array of a plurality of pixels and a backlight light source that irradiates the plurality of pixels, and displays an image including a plurality of frames.

  Conventionally, a display has been developed that includes an optical shutter that moves in binary and controls the output light of the backlight by opening and closing the shutter. In recent years, with the development of MEMS (MicroElectro Mechanical Systems) technology, MEMS displays in which a shutter realized by this technology is provided on a TFT (Thin-Film transistor) substrate have also been developed.

  For example, Dan Van Ostrand and B. C., published on pages 1054-1057 of the SID 2008 digest. “Time Multiplexed Optical Shutter (TMOS) —Advantages & Advanced” (Non-Patent Document 1) by Tod Cox describes a shutter control method for displaying an image on the MEMS display as described above. Within one frame period, the R, G, and B backlight LEDs are turned on in order. By controlling the opening / closing time of the optical shutter during the subframe in which the R, G, and B backlight LEDs are turned on, the gradation expression of each color is achieved.

FIG. 5 represents a gradation representation of a display device with an optical shutter according to the prior art. As shown in FIG. 5, the light intensity of the backlight is always constant throughout one subframe. On the other hand, the time during which the optical shutter is opened is modulated with a ratio of 1: 2: 4: 8: 16: 32: 64: 128 within a period of one subframe. That is, the subframe is divided into eight. Thereby, the display apparatus can express 256 gradations. FIG. 5 illustrates an example of a sequential method in which the R, G, and B backlight LEDs are sequentially turned on within one frame period. Naturally, gradation is determined by opening and closing the optical shutter in units of one frame. Expression is also possible.
Dan Van Ostrand and B.B. Tod Cox, "Time Multiplexed Optical Shutter (TMOS)-Advantages &Advanced", SID 2008 digest, pages 1054-1057

  However, the display device according to the prior art requires a considerably high frequency to drive the optical shutter. The higher the drive frequency, the greater the power consumption, and there is a problem of device failure due to component deterioration or heat generation.

  In view of such a problem, an object of the present invention is to provide an active matrix display device having a drive frequency as low as possible in an active matrix display device having an optical shutter in each pixel.

  In order to achieve the above object, an active matrix display device of the present invention has an array of a plurality of pixels and a backlight light source for illuminating the plurality of pixels, and displays an image including a plurality of frames. In the active matrix display device, a plurality of optical shutters provided in each of the plurality of pixels, a shutter control unit that opens and closes the plurality of optical shutters, and an intensity of light emitted from the light source is 2 The light source control unit that modulates the above multi-stages and the shutter control for modulating the intensity of light emitted from the light source by the light source control unit so as to realize a predetermined gradation expression in one predetermined frame. A synchronization control unit that synchronizes with the opening and closing of the plurality of optical shutters by the unit.

  This makes it possible to provide an active matrix display device having a drive frequency as low as possible in an active matrix display device having an optical shutter for each pixel. As a result, power consumption is reduced, deterioration of components and heat generation are avoided, and the lifetime of the display device can be extended.

Preferably, in one embodiment of the present invention, in the case of realizing gradation expression of M × N (M, N is an integer of 2 or more) bits in the predetermined frame of 1, the light source controller is The intensity of light emitted from the light source is modulated in M stages within a predetermined frame period, and the shutter control unit opens the optical shutter within the predetermined frame period. the times were modulated N stages, the synchronization control unit, the modulation ratio of the time the optical shutter is opened a _x and the modulation ratio I _y of the intensity of light emitted from the light source respectively, the following Equation A _x = 2 ^x (x = 0, 1,..., N−1)
I _y = 2 ^yN (y = 0, 1,..., M−1)
Or A _x = 2 ^xM (x = 0, 1,..., N−1)
I _y = 2 ^y (y = 0, 1,..., M−1)
The light source control unit and the shutter control unit are controlled as determined by

  As described above, the modulation ratio of the time during which the optical shutter is opened and the modulation ratio of the backlight luminance in the period of one frame are obtained according to a certain rule as expressed by the above formula.

  Preferably, in one embodiment of the present invention, the synchronization control unit is configured so that the light source control unit keeps the intensity of light emitted from the light source constant when the optical shutter is opened. The light source controller modulates the intensity of light emitted from the light source so that it is at least longer than the response time of the backlight light source and shorter than or at least equal to the inverse of the frame rate. The shutter control unit synchronizes with the opening and closing of the plurality of optical shutters.

  Thereby, it is possible to avoid the response loss and flicker problem of the backlight light source.

  The active matrix display device according to an embodiment of the present invention may be a MEMS display or a ferroelectric liquid crystal display.

  The optical shutter can be opened and closed mechanically in MEMS displays, while it can be opened and closed electrically in ferroelectric liquid crystal displays.

  According to the present invention, it is possible to provide an active matrix display device having a drive frequency as low as possible in an active matrix display device having an optical shutter for each pixel.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of a display apparatus according to an embodiment of the present invention.

  The display device 1 of FIG. 1 has an array 10 of a plurality of pixels and an active matrix type that displays an image including a plurality of frames (that is, a moving image) having a backlight light source 12 that irradiates these pixels. A display device. Each pixel is provided with an optical shutter, and the transmission of light emitted from the light source 12 is controlled by opening and closing the optical shutter. The optical shutter is opened and closed mechanically or electrically. A typical example of the mechanically controlled opening / closing of the optical shutter is a MEMS display in which a shutter realized by MEMS technology is provided on a TFT substrate. A representative example of the one in which the opening and closing of the optical shutter is electrically controlled is a ferroelectric liquid crystal display that utilizes a change in the orientation of liquid crystal molecules due to the application of an electric field.

  The display device 1 includes a shutter control unit 14 that opens and closes an optical shutter provided in each pixel, a light source control unit 16 that modulates the intensity of light emitted from the light source 12 in two or more stages, and a shutter control unit. 14 and the light source controller 16 are further included. The synchronization control unit 18 uses the light source control unit 16 to realize a predetermined gradation expression by combining the length of time the shutter is open in one predetermined frame and the intensity of light emitted from the light source 12. The modulation of the intensity of light emitted from the light source 12 can be synchronized with the opening / closing of the optical shutter by the shutter control unit 14.

  In the following, a specific example is given, and a predetermined gradation expression can be realized by combining how long the shutter is open and the intensity of light emitted from the light source 12. We will explain in detail what can be done.

  FIG. 2 represents a gray scale representation of a display device according to the first embodiment of the present invention. It should be noted that the display device according to the present embodiment is a monochrome display format, and therefore FIG. 2 shows the state of control in one frame.

As shown in FIG. 2, the shutter control unit 14 modulates the time during which the optical shutter is open into four stages with a ratio of 1: 2: 4: 8 within one frame period. Specifically, one predetermined frame is divided into four subframes, and each subframe is (1/15) × _TF , (2/15), where _TF is the duration of one frame. ) × T _F , (4/15) × T _F and (8/15) × _TF , and are arranged sequentially in the frame.

The light source control unit 16 modulates the intensity of light emitted from the light source 12 (hereinafter referred to as “backlight luminance”) in two stages with a ratio of 1:16 in each subframe. Specifically, when the backlight luminance in the first half period of the subframe is 1, the backlight luminance in the remaining half period is 16 times that of the first half period. Thus, unlike the prior art shown in FIG. 5, in this embodiment, the backlight brightness is not always constant, but alternately changes between two values set to have a ratio of 1:16. To do. Thus, the shortest duration of time that the optical shutter is open within one frame period is (1/30) × _TF, which is half the duration of the first subframe. In this way, the display device according to the present embodiment can express 256 gradations in the same manner as the display device according to the prior art.

On the other hand, in the display device according to the prior art, the shortest duration of the time when the optical shutter is open is (1/255) × _TF , as is apparent from FIG. Therefore, in the display device according to the present embodiment, the frequency required to drive the optical shutter can be lower than the display device according to the prior art.

  In this way, by combining the opening / closing control of the optical shutter with the modulation of the backlight luminance, the driving frequency of the optical shutter can be lowered, and as a result, the power consumption is reduced. Furthermore, the deterioration and heat generation of the parts are avoided, and the lifetime of the display device can be extended.

  FIG. 3 is a table illustrating examples of possible tone representations in a display device according to various embodiments of the present invention. In the table of FIG. 3, for comparison, the gradation representation of the display device according to various embodiments of the present invention (patterns 1 to 15) is shown together with the gradation representation of the display device according to the prior art shown in FIG. It is indicated by a numerical value.

  In the table of FIG. 3, the shaded row (pattern 10) represents a grayscale representation of the display device according to the embodiment shown in FIG. According to this, as described with reference to FIG. 2, the backlight luminance is modulated in two stages, one predetermined frame is divided into four subframes, and gradation is represented by 8 bits. (Ie, 256 gradations), the time during which the optical shutter is opened within the period of one frame is modulated with a ratio of 1: 2: 4: 8, and the modulation ratio of the backlight luminance is 1:16. I understand that. Here, the number of gradation bits is equal to the product of the number of backlight luminance modulation stages and the number of subframes.

  Further, in the table shown in FIG. 3, the luminance realized over the whole period of the unit sub-frame is indicated by a ratio. In the gray scale expression of the display device according to the embodiment shown in FIG. 16 and 17 can be realized. In the subframe, when the optical shutter is closed in both the first half period and the remaining half period, the light emitted from the light source 12 does not pass through the pixel, and the pixel displays black. To do. The luminance at this time is zero. If the optical shutter is opened only during either the first half period or the remaining half period, the brightness in the entire subframe is either 1 or 16. If the optical shutter is open in both the first half period and the remaining half period, the luminance in the entire subframe is 17.

The table further shows the shortest duration of time that the optical shutter is open. In the display device according to the embodiment shown in FIG. 2, as described above, the duration of one frame is shown. In the case of _TF , (1/30) × _TF .

It should be noted that in this case, the number of modulation steps of the backlight luminance is M (≧ 2), and the number of modulation steps of the time when the optical shutter is open, that is, the number of subframes is N (≧ 2). , The synchronization control unit 18 controls the light source control unit 16 and the shutter control so that the modulation ratio A2 _x during which the optical shutter is open and the modulation ratio I2 _{y of the} backlight luminance are determined by the following equations. This is the point that controls part 14:
A2 _x = 2 ^x (x = 0, 1,..., N−1) (1-1)
^{_{I2 y = 2 yN (y =}} 0,1, ···, M-1) (1-2)
According to this equation, in the display device according to the embodiment shown in FIG. 2, the number M of the backlight luminance modulation stages is “2”, and the number N of subframes is “4”. “1, 2, 4, 8” is obtained as the modulation ratio A2 _x of the time during which the optical shutter is opened within the period, and “1, 16” is obtained as the modulation ratio I2 _y of the backlight luminance.

  The above formulas (1-1) and (1-2) include the patterns 8 to 14 shown in the table of FIG. 3 including the pattern 10 indicating the gradation expression of the display device according to the embodiment shown in FIG. This is the case.

In the examples of patterns 1 to 7, similarly, when the number of backlight luminance modulation stages is M (≧ 2) and the number of subframes is N (≧ 2), the optical shutter is within one frame period. The modulation ratio A1 _{x for the} time when is opened and the modulation ratio I1 _{y for the} backlight brightness are determined by the following equations:
A1 _x = 2 ^xM (x = 0, 1,..., N−1) (2-1)
I1 _y = 2 ^y (y = 0, 1,..., M−1) (2-2)
According to this equation, the pattern 2 will be described as an example. The number M of the backlight luminance modulation stages is “2”, and the number N of subframes is “3”. “1, 4, 16” is obtained as the modulation ratio A1 _{x when the} shutter is open, and “1, 2” is obtained as the modulation ratio I1 _y of the backlight luminance.

  As described above, the modulation ratio of the time when the optical shutter is opened and the modulation ratio of the backlight luminance in the period of one frame are expressed by the equations (1-1) and (1-2) or the equations (2-1) and (2-1). It is obtained according to a certain rule as expressed by any of 2-2).

  Exceptionally, the pattern 15 is not obtained by any of the expressions (1-1) and (1-2) or the expressions (2-1) and (2-2). The pattern 15 represents a case where the luminance is modulated in eight steps, and the time during which the optical shutter is open is the same in each luminance modulation step. That is, the number of subframes is “1”. In the above equations (1-1) and (1-2) and equations (2-1) and (2-2), the number M of the backlight luminance modulation stages and the number N of subframes are both 2 or more. It has been found that it can be applied in some cases.

  FIG. 4 represents a gray scale representation of a display device according to the second embodiment of the present invention. It should be noted that the display device according to the present embodiment has a monochrome display format, and therefore FIG. 4 shows the state of control in one frame.

As shown in FIG. 4, as in the first embodiment shown in FIG. 2, the shutter control unit 14 sets the time during which the optical shutter is open to 1: 2: 4 within one frame period. : Modulate with a ratio of 8. However, the modulation periods are sequentially arranged in a ratio of 1: 2: 4: 1: 2: 4: 8: 8 within one frame period. Specifically, assuming that the duration of one frame is _TF , the first to third periods in which the optical shutter is open are (1/30) × T _F and (2/30) × _{TF, respectively.} And (4/30) × T _F having different durations, and the subsequent fourth to sixth periods are similarly (1/30) × T _F , (2/30) × T _F and ( 4/30) × _TF , and the last seventh and eighth periods each have the same (8/30) × _TF duration.

  Further, the light source control unit 16 modulates the backlight luminance in two steps with a ratio of 1:16, as in the first embodiment shown in FIG. However, the backlight brightness is not changed alternately between the two values one by one, but is constant at 1 in the first first to third periods and in the subsequent fourth to fifth periods. 16 is constant, becomes 1 again in the seventh period, and becomes 16 in the final eighth period.

  In this manner, the display device according to the present embodiment can express 256 gradations as in the display device according to the related art.

The shortest duration of the time when the optical shutter is open is (1/30) × _TF , as in the first embodiment shown in FIG. However, the shortest time for the light source control unit 16 to keep the backlight brightness constant when the optical shutter is opened is the first to third periods or the fourth to sixth periods in this embodiment. It corresponds to the length and is ((1 + 2 + 4) / 30) × _TF . This is seven times as long as the first embodiment shown in FIG. In this way, by increasing the shortest time during which the backlight luminance is kept constant, it is possible to avoid the problem of response loss and flicker of the backlight light source 12.

  As the backlight light source 12, an LED is generally used. Since the LED usually takes 100 to 200 ns to rise, the shortest period in which the light source controller 16 keeps the intensity of light emitted from the light source 12 constant is at least the rise time (generally “response time”). It is preferable that the length is longer than that. Conversely, if this shortest period is too long, the drive frequency becomes too low and flicker can occur. Specifically, in order to prevent the occurrence of flicker, it is preferable that the backlight luminance is modulated at a frequency that is greater than or at least equal to a “frame rate” that represents the number of times a frame is updated per unit time.

  The synchronization control unit 18 modulates backlight luminance by the light source control unit 16 so as to determine a combination of optical shutter opening / closing control and backlight luminance modulation so as to avoid the problem of response loss and flicker of the backlight light source. Is synchronized with the opening and closing of the optical shutter by the shutter control unit 14.

  Specifically, in the example shown in FIG. 4, as in the first embodiment shown in FIG. 2, the backlight luminance is modulated in two steps with a ratio of 1:16, and the optical shutter is opened. The time being modulated is modulated with a ratio of 1: 2: 4: 8, but their combination, ie, the arrangement of subframes within one frame period is different. As described above, various combinations of the opening / closing control of the optical shutter and the modulation of the backlight luminance can not only lower the driving frequency of the optical shutter but also avoid the problem of response loss of the backlight light source and flicker. It becomes possible.

  Although the best mode for carrying out the invention has been described above, the present invention is not limited to the embodiment described in the best mode. Modifications can be made without departing from the spirit of the present invention.

  For example, the above-described embodiment of the present invention can also be applied to a sequential method in which R, G, and B backlight LEDs are sequentially turned on within one frame period. The gradation expression described with reference to FIGS. 2 to 4 is realized in the period of the subframe in which the G and B backlight LEDs are turned on.

1 shows a configuration of a display device according to an embodiment of the present invention in a block diagram format. 2 represents a grayscale representation of a display device according to a first embodiment of the invention. 6 is a table illustrating examples of possible tone representations in a display device according to various embodiments of the present invention. 2 represents a grayscale representation of a display device according to a second embodiment of the invention. 2 represents a gradation representation of a display device with an optical shutter according to the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Active matrix type display apparatus 10 Pixel arrangement 12 Backlight light source 14 Shutter control unit 16 Light source control unit 18 Synchronization control unit

Claims (4)

An active matrix display device having an array of a plurality of pixels and a backlight light source for illuminating the plurality of pixels, and displaying an image including a plurality of frames,
A plurality of optical shutters provided in each of the plurality of pixels;
A shutter control unit for opening and closing the plurality of optical shutters;
A light source controller that modulates the intensity of light emitted from the light source in two or more stages;
The light source controller modulates the intensity of light emitted from the light source by the light source controller in synchronization with the opening and closing of the plurality of optical shutters by the shutter controller so as to realize a predetermined gradation expression in one predetermined frame. An active matrix display device having a synchronization control unit. In the case of realizing gradation expression of M × N (M and N are integers of 2 or more) bits in the predetermined frame of 1,
The light source control unit modulates the intensity of light emitted from the light source into M stages within a period of the predetermined frame of 1,
The shutter control unit modulates the time during which the optical shutter is opened in N stages within the period of the one predetermined frame,
The synchronization control unit is configured such that a modulation ratio A _x when the optical shutter is opened and a modulation ratio I _y of the intensity of light emitted from the light source are respectively expressed by the following expressions A _x = 2 ^x (x = 0, 1, ..., N-1)
I _y = 2 ^yN (y = 0, 1,..., M−1)
Or A _x = 2 ^xM (x = 0, 1,..., N−1)
I _y = 2 ^y (y = 0, 1,..., M−1)
The active matrix display device according to claim 1, wherein the light source control unit and the shutter control unit are controlled as determined by:   The synchronization control unit has at least a response time of the light source for backlight when the light source control unit keeps the intensity of light emitted from the light source constant when the optical shutter is opened. The light source controller modulates the intensity of light emitted from the light source so that it is longer or shorter than the reciprocal of the frame rate. The active matrix display device according to claim 1, wherein the display device is synchronized with the active matrix display device.   4. The active matrix display device according to claim 1, wherein the active matrix display device is a MEMS display or a ferroelectric liquid crystal display.

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